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SA 9500II Issue: New Thread Old Problem: I Need Help Please!!!!

Kingbuuba
Here is the readings you have last posted for the left and right check the voltages on the right and see if they are still this way.

Code: 
AWH-052 L               AWH-052 R  
Q6                      Q6
C  -52.75               C -51.56  (-51.4)
B  -1.15                B -1.16  (-1.2)
E  -.6                  E -.60  (-0.6)

Q5                      Q5
C  +52.6                C +51.4  (51.4)
B  +1.09                B +1.09  (1.2)
E  +.55                 E +.53  (0.6)

Q4                      Q4
C  +1.0                 C +1.1  (1.2)
B  +46.81               B +46.4  (46.6)
E  +47.5                E +47.05  (47.2)

Q2                      Q2
C  +13.5                C +7.08  (5.0)
B  -47.37               B -46.9  (-46.4)
E  -47.99               E -47.5  (-47.0)

Q3                      Q3
C  -1.13                C -1.16  (-1.2)
B  -47.7                B -46.9  (-46.4)
E  -47.99               E -47.5  (-47.0)

Q1                      Q1
C  -47.1                C  -47.2 and -47.1  (-46.4)
B  +.03                 B  +.033 and +.031  (0.0)
E  +.65                 E  +.65  (0.6)
 
It may be a few day before this can happen. I am about to go into another "Hell" week here at work. I'm still in no hurry. Thanks for the suggestion.
 
Here are the differences:

AWH-052 L _________AWH-052 R
Q6 __________ Q6
C -52.75 _________ C -51.56 (-51.4) now -53.2
B -1.15 __________ B -1.16 (-1.2) now -14.83
E -.6 ___________ E -.60 (-0.6) now -14.49

Q5 ___________ Q5
C +52.6 __________ C +51.4 (51.4) now +53.15
B +1.09 ___________ B +1.09 (1.2) now -12.38
E +.55 ____________ E +.53 (0.6) now -0.12

Q4 ____________ Q4
C +1.0 ____________ C +1.1 (1.2) now -12.37
B +46.81 ____________ B +46.4 (46.6) now +46.55
E +47.5 ____________ E +47.05 (47.2) now +47.15

Q2 ____________Q2
C +13.5 ____________ C +7.08 (5.0) now +9.0
B -47.37 ____________ B -46.9 (-46.4) now -46.93
E -47.99 ____________ E -47.5 (-47.0) now -47.58

Q3 _____________ Q3
C -1.13 _____________ C -1.16 (-1.2) now -14.8
B -47.7 ______________ B -46.9 (-46.4) now -46.9
E -47.99 _____________ E -47.5 (-47.0) now -47.58

Q1 _____________Q1
C -47.1 _____________ C -47.2 and -47.1 (-46.4) now -46.9 and -46.9
B +.03 ______________ B +.033 and +.031 (0.0) now +.033 and +.033
E +.65 ______________ E +.65 (0.6) now +.62

I must say I am surprised at the fact that this side of the amp functions normally and sounds as good as I can remember it sounding in the past. I have, however, not pushed it very hard and I am only using a pair of Insignias.

At any rate, can anyone give me an idea where the issue lies from this information or am I back to removing everything and testing it out of circuit again. Thanks for any assistance on this.
 
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Just a bump. Trying to keep this old thread alive long enough to get this beast fixed once and for all. :yes: :D
 
KingBubba said:
Here are the differences:

AWH-052 L _________AWH-052 R
Q6 __________ Q6
C -52.75 _________ C -51.56 (-51.4) now -53.2
B -1.15 __________ B -1.16 (-1.2) now -14.83
E -.6 ___________ E -.60 (-0.6) now -14.49

Q5 ___________ Q5
C +52.6 __________ C +51.4 (51.4) now +53.15
B +1.09 ___________ B +1.09 (1.2) now -12.38
E +.55 ____________ E +.53 (0.6) now -0.12

Q4 ____________ Q4
C +1.0 ____________ C +1.1 (1.2) now -12.37
B +46.81 ____________ B +46.4 (46.6) now +46.55
E +47.5 ____________ E +47.05 (47.2) now +47.15

Q2 ____________Q2
C +13.5 ____________ C +7.08 (5.0) now +9.0
B -47.37 ____________ B -46.9 (-46.4) now -46.93
E -47.99 ____________ E -47.5 (-47.0) now -47.58

Q3 _____________ Q3
C -1.13 _____________ C -1.16 (-1.2) now -14.8
B -47.7 ______________ B -46.9 (-46.4) now -46.9
E -47.99 _____________ E -47.5 (-47.0) now -47.58

Q1 _____________Q1
C -47.1 _____________ C -47.2 and -47.1 (-46.4) now -46.9 and -46.9
B +.03 ______________ B +.033 and +.031 (0.0) now +.033 and +.033
E +.65 ______________ E +.65 (0.6) now +.62

I must say I am surprised at the fact that this side of the amp functions normally and sounds as good as I can remember it sounding in the past. I have, however, not pushed it very hard and I am only using a pair of Insignias.

At any rate, can anyone give me an idea where the issue lies from this information or am I back to removing everything and testing it out of circuit again. Thanks for any assistance on this.
Click to expand...

Looks like Q3 may be bad. Take it out and test it.
If it tests good test Q4
Ohm out the bias pot VR1
Verify the STV4H D2 is not broken.
 
Q3 tests good, Q2 tests good, Bias pot is good. The bias diode, as noted in post #4 of this thread has a small chip in it. When testing with a meter in diode setting, it shows OL in both directions, however, if tested with a meter in ohm setting it tests OL one way and 1.2 M ohm the other way. :scratch2: This was the reading out of circuit.

I did an in circuit test and the left(good) side showed 21.2 M ohm one way and 656 K ohm the other way. The right(questionable) side showed OL and 886 M ohm. :scratch2: :scratch2: Not knowing if the VR might have some bearing on this reading from the right, I zeroed the pot and reread the bias diode readings on right. There was no difference.
 
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KingBubba said:
Q3 tests good, Q4 tests good, Bias pot is good. The bias diode, as noted in post #4 of this thread has a small chip in it. When testing with a meter in diode setting, it shows OL in both directions, however, if tested with a meter in ohm setting it tests OL one way and 1.2 M ohm the other way. :scratch2:
Click to expand...

Gary
can you take some ohm readings comparing the good side
with the bad
we are looking for the differene around q2-q6
also compare that stv4 diode
 
Goat67, see post #66 for an edit that includes readings from the left side. Further testing on the left side requires dis-assembly which I may not be able to get to today.
 
KingBubba said:
Q3 tests good, Q4 tests good, Bias pot is good. The bias diode, as noted in post #4 of this thread has a small chip in it. When testing with a meter in diode setting, it shows OL in both directions, however, if tested with a meter in ohm setting it tests OL one way and 1.2 M ohm the other way. :scratch2: This was the reading out of circuit.

I did an in circuit test and the left(good) side showed 21.2 M ohm one way and 656 K ohm the other way. The right(questionable) side showed OL and 886 M ohm. :scratch2: :scratch2: Not knowing if the VR might have some bearing on this reading from the right, I zeroed the pot and reread the bias diode readings on right. There was no difference.
Click to expand...

On the last readings where both in circuit?
 
Replace Q2, Q3 and Q4 with NEW ones at the same time. While doing it, and they are out, check all the resistors connected to them, with a lead raised if anything else is connected at that end of the component.

I have lost count of the number of times a transistor has tested good, yet failed to work in the circuit. Compound that with several interacting transistors and it gets frustrating fast. Plus in a piecemeal approach, new ones can be damaged instantly.

You are working with a circuit that has multiple compensating effects - a differential amplifier (Q2 & Q3) with a current mirror(Q4) for the collector loads.

I have seen half-dead diff amps struggle along and "somewhat" work.

As for the STV-4H readings, is the battery in your meter fresh? The diode test may not have enough voltage to push a current through. It IS spec'd at 2.1 to 2.3v at 7mA Ifwd and my meter, at a lower test current shows 1.85 volts or so.
 
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All transistors on the right board have been tested and are good. All resistors test good. All diodes test good. Bunged up the trace on Q6; I'm pissed. :nono: I'll look for replacements for Q2>4. I will also replace batteries in the meter and double check the readings Thanks for the help.
 
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Do not get down on yourself we all have that kind of stuff happen.
You will be able to correct it.
Do you need part numbers from Mouser on the transistors?
I am going out to dinner now but if you need them I can try and see what I can find out.
I am sure Mark has posted them some where.
 
For Q4, the pnp 2sa898, an OnSemi MJE350 looks like a reasonable choice, but I am open to all suggestions. The npn, a 2sc1903, is another story entirely. I can find no datasheets and none of the usual suspect's cross references are of any help, including B+D. The SM also lists a 2sc1885S or R as a replacement. It also is not showing up anywhere.

I am looking for a to-225 or a similar style npn transistor. A to-220 should fit okay. The only info I have to go by is the sheets that Echowars made available in .doc format. The 2sc1903 shows the following on that sheet:
Vceo:150 Ic: 0,050 Pc: 1,000 B: 150 Ft: 130

I presently have in my stash of new NPN transistors:

mje15032
BD239C
BD239BTU
KSC945CGBU

For PNPs I have:

mje15033
FJP1943OTU
KSA940
BD240BTU

I have the datasheets at home so I won't take the time now to look up the specs. If any of these ring a bell as a replacement, let me know.


I am posting a warning because in searching for datasheets I have come across an unusual situation. After going to a number of googled links of places that were dead ends, I have now suddenly developed a major problem with Firefox. If I now click on certain links Firefox just shuts off immediately. There is no rhyme or reason. Some links are fine but others just cause Firefox to stop and disappear. Since the time it happened first, I have updated Firefox, restarted the computer, run a full malware scan with Malewarebytes. Avast is still running and has found some rootkit malware. I am now very suspicious of some of the sites I visited but have no idea which one may be the source of the issue, or even it was a site that was the source of the issue.

This is the link that shuts me down right away:

datasheetarchive

I don't know that this site is suspect; it may be the previous sites that interjected the problem, but this is the site that shuts down Firefox right away. This is not the only site that has brought on the shut down response.

I am starting a thread about this to make AK aware of a potential issue with datasheet searches.
 
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When I first visited that site a long time ago I was also suspicious but it has never done my any harm.
If you are using windows, do a search for advanced care for windows, a free anti-spyware program. I also run Malewarebytes but advanced just seems to find stuff where Maleware doesn't.
 
Here is what I recommend from Mouser

2SC1903
512-MJE340STU

also could use Fairchild KSC2682 but obsolete

2SA898
512-MJE350STU

Also could use Fairchild KSA1142
 
q1 2sa798 a b
dual transistor

q2,3 2sc1903 xxx to-126 ecb 150v 50mA 1W 150hfe 130mhz
q4 2sa898 xxxxxx to-126 ecb 150v 50mA 1W 150hfe 100mhz
512-KSA1381es x to-126 ecb 300v .1a x 1.2/7w 150mhz 40-320hfe $0.27 ea
512-KSC3503estu to-126 ecb 300v .1a x 1.2/7w 150mhz 40-320hfe $0.28 ea
(these are standard #'s as well: 2sa1381/2sc3503)


q5 2sd381 driver to-220 bce 120v 1.5a 40-250hfe 40mhz
q6 2sb536 driver to-220 bce 120v 1.5a 40-250hfe 40mhz
512-KSA940TU_Q pnp to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.54
512-KSC2073TU npn to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.54
or
863-MJE15033G pnp to-220 bce 250v 8a 50w 30mhz 70hfe $0.87
863-MJE15032G npn to-220 bce 250v 8a 50w 30mhz 70hfe $0.87
 
Thanks Goat67 and Mark for the time savers. I may as well put together my SX 1250 order now and just tack these on at the end. I finally got a day off today so I'll pick up again when I get back at work with the new batteries in the meter. I did some research on the stv4h and get the feeling, if I need a new one of those, I am SOOL. All this manipulation can't be good for the stinky little wires on those. I've tried to be as careful as possible with them.
 
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